Recently, large-scaled roads such as beltline highways have been constructed around metropolitan regions in order to meet an increased traffic volume. Further, there have been required designs of the roads for minimizing right of way in order to meet recent requirements of a tunnel having a large cross-section and increased price of land.
Moreover, since a large portion of Korea is mountainous, there have been required tunnel-bridge structures so as to improve linearity of roads and obtain good linearity of roads in designing the roads.
A conventional tunnel having total four lanes is designed such that an up-tunnel and a down-tunnel are spaced from each other by a distance of 30 m or more in consideration of arching of an original ground, thus requiring an excessively large area for constructing the tunnel.
In case that the conventional tunnel is designated such that two tunnels, i.e., the up-tunnel and the down-tunnel, are close to each other, pillars are installed between the two tunnels. The pillars have a reduced stability due to water leakage from a ceiling area of the tunnel and the occurrence of freezing in the winter season. These phenomena occur due to failure of drainage at a low point of an upper end of an intermediate area of the two main tunnels.
That is, as shown in FIG. 2a, which is a schematic cross-sectional view of a conventional pillar-supporting type two arch tunnel, the conventional pillar-supporting type two arch tunnels comprises pillars for supporting the tunnel are installed between two main tunnels, thus having a weak structure. Further, the conventional pillar-supporting type two arch tunnel comprises drain pipes respectively installed in the pillars so that subterranean water contained in the ground around an upper portion of the tunnel is eliminated therethrough. However, the subterranean water is gathered in low-level areas (low points) of the ceiling area and is not easily drained, thus generating subterranean water leakage and whitening the surface of the areas.
When the pillars are constructed from concrete, the pillars must be constructed such that respective portions of the pillars, i.e., base portions, wall portions and upper haunch portions, are divisionally constructed. Thus, the conventional tunnel is disadvantageous in that the number of constructing steps is increased and a long construction period is taken.
Further, since the pillars of the conventional tunnel are separated from the ceiling area by a waterproof layer, the pillars are fixed to the tunnel not by hinges or fixing points but by free terminals and the filling of a grout material is incompletely performed.
As shown in FIG. 2b, which is an assembled cross-sectional view of reinforcing bars of an intermediate wall of a conventional three arch excavated tunnel, construction of clamp joint steels between the intermediate wall and lining concrete causes complexity in installing a mold and placing concrete and a difficulty in construction, thus deteriorating quality of the pillars when the concrete is placed.
Further, when main tunnels of the conventional tunnel are excavated by blasting, a vibration damping method for protecting the ground located at top portions of the pillars is not applied. Accordingly, the excavation of the conventional tunnel easily damages the ground.